The present invention relates to turbochargers used in conjunction with internal combustion engines and in particular to a control system for a turbocharger responding to intake and exhaust manifold pressure.
Normally, higher engine speeds result in higher turbocharger speeds with corresponding increases in compressor/intake manifold pressures. In addition, increasing the engine load at a constant engine speed results in increased exhaust gas temperature and increased gas flow thereby increasing turbocharger speed.
Since the limiting factor in turbocharging and internal combustion engine design is the maximum cylinder pressures that may be encountered, problems have resulted from the attempts to balance these maximum pressures with maximum design efficiency.
Pressure developed by a centrifugal turbocharger varies as the square of the speed. The exponential pressure increment that will render rapid boost at lower engine speeds will become a liability at higher speeds since it will inordinately raise cylinder pressures above design levels. In addition, excessive combustion chamber pressures and temperatures will increase the Nitrogen Oxide (NO.sub.x) exhaust emissions above desireable levels.
In order to control cylinder pressures, various types of wastegates have been developed to limit the compressor/intake manifold boost pressure. This allows desireable boost at lower engine speeds with constant boost as engine speed increases. The limiting design factor, however, is still the combustion chamber pressure generated at the highest design speed of the engine. This limiting factor is due to the fact that cylinder pressure increases with engine speed.
One popular means by which engine manufacturers have dealt with the problem is to reduce the compression ratio of an engine when incorporating a turbocharger. This allows an increase in the boost pressure while the combustion chamber pressure remains at approximately the same level at the highest engine speed. This approach, of course, requires a redesigned engine with much of the same design limitations.
The most desirable turbocharged engine is one that can achieve maximum boost pressure and therefore torque at a lower engine speed with a corresponding decrease in boost pressure as engine speed increases to its maximum design speed. This arrangement eliminates the necessity to reduce the engine compression ratio while simultaneously maintaining engine life.
Another advantage is that the high torque corresponding to the higher compressor/intake boost pressures is not as important at high engine RPM as at low engine RPM since acceleration and torque are more desireable at lower engine speeds. This is particularly true in automotive applications when the automobile approaches highway access ramps and in passing situations.
It is the primary object of the present invention therefore to provide for an improved turbocharger control arrangement.
A further object of this invention is to limit the maximum engine combustion chamber pressure at high engine speed and thereby increase the life of the turbocharged engine.
A further object of the present invention is to employ the control unit as an additional Exhaust Gas Recirculating (EGR) mechanism by which part of the control system is used as an EGR when the intake manifold pressure is less than than the exhaust manifold pressure.
A further object of the present invention is to allow turbochargers to be incorporated into internal combustion engines without changes in the original compression ratio of the engine and to maintain the combustion chamber pressure at high engine speeds at a value that does not exceed that of a redesigned engine with a lower compression ratio.
Another object of the present invention is to minimize cylinder detonation when using less than optimum octane fuels.
Still other objects of the invention will become apparent upon a reading of the detailed specifications to follow.